What do you mean "built-in containers"? AFAIK, there's no way to interact with the built-in containers without an extension to expose it. That was at least true when it launched (e.g. the Facebook container extension was awesome), and I've been using the multi-account containers extension ever since.
Here's how I use it:
- no container - no logins at all
- "personal" - my email and related things
- "work" - work email and related things
- "shopping" - online stores
- "financial" - banking and investments
And so on. Each group has limited access to cookies to scrape. I also have accounts at the same service in different containers and can have them side-by-side.
If this is now built-in, awesome! But I was under the impression that you need some form of extension to access it.